I didn't make it past the OA. The OA was automatically sent. The OA was very hard. It was only two questions but it was super hard. Apply at your own risk.
No offer
Positive experience
Difficult interview
Application
I interviewed at Citadel (New York, NY) in Jan 2026
Interview
1. Algorithmic clarity
Can you identify the core pattern quickly?
Think: prefix sums, sliding windows, graph traversal, greedy with proof, DP state design.2. Mathematical reasoning
They love problems where correctness requires a proof or invariant.
Example: why a greedy choice works, why a hash remainder trick detects divisibility.
3. Performance instincts
You’re expected to reason about:
Time complexity under constraints
Memory vs speed tradeoffs
Edge cases at scale (10⁶–10⁹ inputs)
This is finance engineering. Latency is money.
Interview questions [1]
Question 1
1. Prefix sum + hashing
Why? O(1) lookups under heavy data flow.
Examples:
Subarray sum divisible by k
Longest equal 0/1 subarray
Detect arbitrage-like patterns
What they care about:
Do you understand why equal remainders imply divisible differences?